This invention relates to an apparatus for providing access to a containment vessel or the like when closely surrounded by a structure, conforming generally to the shape of the containment vessel, employed for shielding, cooling, and like purposes. More particularly, the invention is directed to a containment vessel or the like surrounded by a disparate shield building forming an air annulus with an air baffle positioned in the air annulus. A movable portion of the air baffle provides access from the exterior to the containment vessel by being movable up and away from the containment vessel toward the shield building.
A nuclear power generating station is divided into two basic systems, a containment vessel containing the nuclear core for heating a coolant, such as water, and a steam utilization system containing a steam utilization and conversion means, such as a steam turbine-generator system. In a power plant of the pressurized water reactor type (PWR) two separate coolant flow systems are provided in heat exchange relationship with each other, while in a power plant of the boiling water reactor type (BWR), a single or primary coolant flow system having a light water coolant is employed, which coolant is heated by the reactor core so that it is converted to steam and the steam directly operates the steam turbine of the steam utilization and conversion means. In both the PWR and BWR types, the reactor vessel and certain auxiliary equipment are contained in a separate structure, called a containment, because nuclear reactions producing radiation are occurring and must be contained in a structure with extremely rigid standards to contain the radiation in the unlikely event of an accident. The separate containment typically has one of two designs. One design comprises a unitary containment vessel typically made of concrete with a steel liner. The second design comprises a two tier structure comprising a steel structure, referred to herein as the containment vessel, disposed within a separate concrete building called a shield building. Within the containment vessel, the reactor core is disposed inside the reactor vessel and includes uranium pellets used in the nuclear reaction which generates heat. A coolant such as light water is circulated through the nuclear core reaction area. In the PWR type system, the coolant circulates in a loop entirely within the containment and transfers the heat from the nuclear core to the secondary system steam turbine located outside of the containment. In the BWR type, the heated coolant exits the containment as steam in a single system and flows directly to a steam turbine located outside of the containment.
In systems employing the two tier design including a containment vessel disposed within a shield building, an apparatus is needed to remove the ambient heat surrounding the containment vessel during the unlikely event of an accident. To accomplish such heat removal, a system such as a passive containment cooling system may be used. Passive containment cooling uses natural air circulation to remove the heat by flowing air into a shield building and over the surface of the containment vessel and then out of the shield building. To minimize the cooling space surrounding the containment vessel, an air baffle is positioned close to the containment vessel. During non-operational periods the containment vessel may require maintenance, inspection and the like. Because the air baffle is positioned close to the containment vessel, inspection is restricted due to the limited space between the air baffle and the containment vessel.
U.S. Pat. No. 5,049,353 issued on Sep. 17, 1991 teaches a passive cooling system in which the air baffle in conjunction with cooling water form a system of providing a passive cooling system. This patent teaches a disparate shield building surrounding and containing a containment vessel forming an air annulus in the space between the shield building and the containment vessel. To create a circulation path, an air baffle is positioned in the air annulus forming an inner and outer annulus. Natural air flows into the shield building through openings located in the shield building wall at the intersection of the roof and wall and down the outer annulus and around the bottom of the air baffle. Next, the air flows up the inner annulus adjacent the containment vessel and exits through an opening in the shield building roof. The cooling water located in the roof portion of the shield building, may be used inside the shield building for additional cooling. This cooling water is sprayed under the forces of gravity onto the containment vessel. However, U.S. Pat. No. 5,049,353 does not disclose an apparatus which will allow maintenance workers and the like to inspect, repair, and the like in the area surrounding the containment vessel.
The present invention teaches a passive containment cooling system, such as in U.S. Pat. No. 5,049,353, and adds advantages such as an air baffle being movable located surrounding a major portion of the containment vessel. When inspection or the like is needed, the movable air baffle moves up and away toward the shield building allowing access to the containment vessel.
The present invention has several advantages over the prior art. First, it provides accessibility to the containment building for maintenance and the like during non-operation. This access is advantageous because of the nominal outage time available for performing preventive maintenance procedures when repairs are needed.
Another advantage is the efficient means in which access is provided. Partial access to sections of the containment vessel is provided by partitioning of the air baffle. This further enhances preventive maintenance, nominal outage during repairs, and the like.